The use of molecular sieves as catalysts in aromatic conversion processes are well known in the chemical processing and refining industry. Aromatic conversion reactions of considerable commercial importance include the alkylation of aromatic compounds such as in the production of ethyltoluene, xylene, ethylbenzene, cumene, or higher alkyl aromatics and in disproportionation reactions such as toluene disproportionation, xylene isomerization, or the transalkylation of polyalkylbenzenes to monoalkylbenzenes. Often the feedstock to such an aromatic conversion process will include an aromatic component, such as benzene, and a C.sub.2 to C.sub.4 olefin alkylating agent or a polyalkyl aromatic hydrocarbon transalkylating agent.
The catalysts for such alkylation or transalkylation reactions generally comprise zeolite molecular sieves. Innes et al., U.S. Pat. No. 4,891,458 discloses the presence of a catalyst comprising zeolite beta. Shamshoum et al., U.S. Pat. No. 5,030,786 discloses an aromatic conversion process employing zeolite Y, zeolite omega and zeolite beta molecular sieve catalyst. Ward et al., U.S. Pat. No. 4,185,040 discloses the alkylation of benzene to produce ethylbenzene or cumene employing zeolites such as molecular sieves of the X, Y, L, B, ZSM-5 and Omega crystal types. Barger et al., U.S. Pat. No. 4,774,377, discloses an aromatic conversion process involving alkylation over a catalyst comprising a solid phosphoric acid component followed by transalkylation using aluminosilicate molecular sieve transalkylation catalysts including X, Y, ultrastable Y, L, Omega, and mordenite zeolites. The above U.S. Patents are hereby incorporated by reference.
Molecular sieve catalysts employed in alkylation reactions in the vapor or the liquid phase may be sensitive to impurities such as water at various levels or sulfur compounds in the feedstock. Dwyer, U.S. Pat. No. 4,107,224, discloses that water and hydrogen sulfide in vapor phase reactions may be tolerable if more rapid aging of the catalyst is acceptable. Shamshoum et al, ibid, disclose the dehydration of the feedstock to a water content of no more than 100 ppm, and preferably 50 ppm or less when the reaction zone is operated to maintain the reactor contents in the liquid phase.
The drying of hydrocarbon liquids is generally accomplished by adsorption of the water by passing the liquid over a suitable adsorbent such as activated alumina, silica gel, or fuller's earth. In the drying of liquids, the wet liquid is passed through one chamber while another is being dried. The feed is usually passed upwardly through the chamber so that slugs of water laden liquid may settle before it contacts the adsorbent. The spent adsorbent is regenerated by draining or steaming the liquid from the adsorbent and passing hot gas or superheated steam through the adsorbent at elevated temperatures.
Fractionation is widely used for drying liquids that are substantially immiscible with water such as propane or hydrocarbon oils. The low boiling product of such a system is a constant boiling mixture of water and the hydrocarbon in proportion to their relative vapor pressure. Upon condensation the constant boiling mixture separates into a hydrocarbon layer and a water layer.
Funk et al., U.S. Pat. No. 5,220,102 disclose a chromatographic process for separating linear olefins from mixtures of branched olefins with a high silica zeolite molecular sieve, e.g., silicalites, ZSM-5, etc., having low acid catalyst reactivity which selectively adsorbs the normal olefins and uses ketones as desorbents.
Flanigen et al., U.S. Pat. No. 4,073,865 disclose a silica polymorph and a process for preparing the silica polymorph having a fluoride content and a low alumina content. The presence of the fluoride anion and the low alumina content in such fluoride-silicalites (F-silicalites) provide a crystalline silica composition which is extremely hydrophobic and is useful for separations requiring minimum water adsorption in the adsorption of less polar materials or where the presence of surface hydroxyl groups or adsorbed water would react with or catalyze reactions of the feed and/or product streams. The U.S. Pat. Nos. 4,073,865 and 5,220,102 are hereby incorporated by reference.
Gorawara et al., U.S. Pat. No. 5,271,835, discloses the presence of polar impurities in the C.sub.3 -C.sub.5 product fraction from a fluid catalytic cracking unit. The impurities were found to include nitrogen compounds such as acetonitrile.
When impurities are present in the feedstock to an aromatic conversion reactor, particularly basic impurities such as nitrogen compounds, the catalyst performance and the catalyst life may be adversely affected. As more active zeolite catalysts are employed in aromatic conversion reactions, the degradation of catalyst life by nitrogen impurities in the feedstock must be more carefully controlled. Processes are sought to reduce the impact of nitrogen impurities on the catalyst in the reaction zone.